Calender

Abstract: The invention concerns a calender, comprising a calender frame (11,12) and a stack of rolls mounted on the frame and consisting of four rolls (13,14,15, 16) fitted one above the other, in which stack the rolls placed one above the other can be fitted in nip contact with one another so as to calender the paper web (W) or equivalent in said nips (N₁,N₂,N₃,). The stack of rolls in the calender is composed of three variable-crown rolls (13,14,16), of which rolls the roll mantle (17) of at least one roll (13) can be displaced in relation to the roll axle (18) in the direction of the nip plane by means of loading devices (19) fitted inside said roll, as well as of one heatable roll (15), which is fitted between two variable-crown rolls (14,16) in the stack of rolls. The roll is preferably arranged so that, in the stack of rolls, the lowest, i.e. the first roll (13), the second roll (14), and the topmost, i.e. the fourth roll (16) are variable-crown rolls and that the third roll (15) in the stack of rolls is a heatable roll.

Description: The invention concerns a calender according to the preamble of claim 1, which is based on the disclosure of the paper "control of a deckling calender", Joseph A. Picard and Dominic A. D'Amato, published in the Tappi Journal (vol. 66 (1983) Febr., No. 2, Atlanta, Georgia, USA, pages 81-84). The calender described therein comprises a stack of four rolls, of which the lowermost and the uppermost are variable-crown rolls while the intermediate rolls are temperature-controlled rolls. High requirements are imposed on a modem calender concerning loading capacity and mode of calendering so as to provide the desired properties of quality on paper. For example, in the course of years, the standard newsprint has developed into several different quality categories, each of which requires a different mode of calendering of its own. High requirements have been imposed on the calender especially by these several quality categories, and it has not been possible to meet these requirements by means of earlier calender arrangements. This factor has also contributed to making soft calenders with two nips ever more common. Both nips of the calender are independent in such a calender with two nips, so that the loads and the temperatures of rolls can be as desired. Drawbacks of the soft calender with two nips have been, for example, the high cost of the solution and that a calender which consists of separate nips has taken very much space in the machine direction. Environmental requirements have become stricter recently, which has had the consequence that paper is recycled to an ever greater extent by producing recycled stock out of reclaimed paper. The introduction of recycled stock and, further, the change over to ever thinner grammages in paper grades set their own strict requirements on the calender. The object of the present invention is to provide a calender of a novel type, which solves the above problems and which novel calender is suitable for calendering of several different types of paper. In view of achieving this, the calender in accordance with the invention is mainly characterized in that the second roll from the bottom of the stack is a variable-crown roll. By means of the invention, it is possible to obtain a number of significant advantages in relation to the prior art, of which advantages the following will be brought up in this connection. The calender in accordance with the invention can be varied from the basic concept to four different alternatives, so that the calender is highly versatile and is suitable for several different paper grades. A calender in accordance with the invention with four rolls has three nips in the basic concept, but additionally it is also possible to operate the calender in accordance with the invention with two nips or one nip. The adjustability of the calender in accordance with the invention in relation to the linear loads in the nips is very good, so that, due to this adjustability, very large linear load ranges can be controlled by means of the calender, whereby, by using one and the same calender, it is possible to calender several different paper grades. In the prior art, it has not been possible to obtain such a great adjustability by means of one calender, but different calenders have had to be constructed for calendering of different types of paper. The other advantages and characteristic features of the invention will come out from the following detailed description of the invention. In the following, the invention will be described by way of example with reference to the figures in the accompanying drawing. Figure 1 is a fully schematic and partly sectional side view of a calender in accordance with the invention. Figures 2A,2B and 2C are schematic side views of the stack of rolls in a calender in accordance with the invention illustrating different running alternatives of the calender. Figures 3A,3B and 3C are views, corresponding to Figs. 2A,2B and 2C, of the stack of rolls in a calender in accordance with the invention illustrating especially how it is possible to control large ranges of linear load by means of the calender in accordance with the invention. In Fig. 1, the calender in accordance with the invention is denoted generally with the reference numeral 10. The calender 10 is a vertical calender with four rolls, comprising a calender frame 11,12, on which frame four rolls 13,14,15,16 of the calender are mounted as a stack of rolls so that said rolls form three calendering nips N 1 ,N 2 ,N 3 between them, through which nips the paper web W is arranged to run. Thus, the stack of rolls in the calender 10 consists of four rolls placed one above the other, of which rolls the lowest, i.e. the first roll 13, the second roll 14, which forms a calendering nip N 3 with the first roll 13, and the highest or fourth roll 16 of the stack of rolls are variable-crown rolls, favourably rolls adjustable in zones. Of said variable-crown rolls, at least the roll mantle 17 of the lowest roll 13 can move radially in relation to the axle 18 of the roll concerned in the direction of the nip plane. Favourably all the variable-crown rolls 13,14,16 are constructed so that their roll mantle 17,21,34 can be displaced radially in relation to the roll axles 18,22,35 in the direction of the nip plane. The roll mantle 17,21,34 of these variable-crown rolls, especially the rolls adjustable in zones 13,14,16, is supported on the roll axle 18,22,35 by means of hydraulic loading devices 19,23,36, by means of which the roll mantle 17,21,34 of said rolls 13,14,16 can be loaded in the direction of the nip plane in order to produce the desired linear loads in the calendering nips N 1 ,N 2 ,N 3 . Such rolls adjustable in zones are known in themselves, and they have been described earlier, for example, in the applicant's earlier FI Patents Nos. 79,177 and 79,178. The third roll 15 in the stack of rolls, which forms calendering nips N 1 and N 2 with the second and the fourth roll 14,16 in the stack of rolls, is a hard-faced, heatable roll, which, in the embodiment shown in the figures, comprises a roll mantle 26 arranged revolving on the axle 27 so that an intermediate space 28 remains between the axle 27 and the roll mantle 26, into which space the heating medium for the heating of the roll 15 is passed. Such rolls are also in themselves known in the prior art. The heatable roll can also be different by its construction, for example, so that ducts passing substantially in the axial direction from one end to the other end of the roll have been formed in the roll mantle 26, in which ducts the heating medium is arranged to circulate. The heating of the roll can also be arranged in other known ways. The rolls 13,14,15,16 in the stack of rolls are mounted on the calender 10 as follows. The two lowest rolls in the stack of rolls, i.e. the first 13 and second roll 14, are mounted in stationary positions. Thus, the bearing housings 20 of the first roll 13 are mounted directly on the calender frame 12. The bearing housings 24 of the second roll 14 are also mounted stationarily in relation to the calender frame 11, so that these bearing housings 24 are suspended rigidly on the supports 25 mounted on the calender frame 11. The third roll 15, i.e. the heatable roll, in the stack of rolls, is mounted on the calender 10 by attaching the bearing housings 29 of the third roll 15 to the loading arms 30, which are mounted pivotally, by means of articulated joints 31 in the axial direction of the roll 15, on fastening brackets 32 arranged on the frame 11 of the calender. Loading cylinders 33 are attached to the opposite or free ends of the loading arms 30, by means of which loading cylinders 33 it is possible to pivot the loading arms 30 around the articulated joints 31. It is possible to adjust the linear load in the second nip N 2 by means of the loading arms 30 and the loading cylinders 33, and further, it is possible to open said second nip N 2 by means of the loading arms 30 and the loading cylinders 33. Similarly, the topmost, i.e. the fourth roll 16, in the stack of rolls is mounted on the calender frame 11 by attaching the bearing housings 37 of the fourth roll 16 to the loading arms 38, which are mounted pivotally by means of articulated joints 39 in the axial direction of the roll 16 on the fastening brackets 40 which are attached to the calender frame 11. Loading cylinders 41 are arranged at the opposite or free ends of the loading arms 38, which loading cylinders 41 are supported on the calender frame 11 from the other end. By means of said loading arms 38 and loading cylinders 41, it is possible to load the first nip N 1 in the calender, and, additionally, it is possible to open said first nip N 1 by means of said devices. In the basic construction of the calender 10 in accordance with the invention, the two lowest rolls in the stack of rolls, i.e. the first roll 13 and the second roll 14, are provided with drives. This is the case especially when all the rolls 13,14,15,16 of the calender 10 are hard-faced rolls. In the calender, it is also possible to arrange a drive on the topmost, i.e. the fourth roll 16 in the stack of rolls. Then, it is possible to provide said fourth roll with a resilient coating. In such a solution, in which the fourth roll 16 is provided with a resilient coating, the threading of the web W into the middle nip, i.e. into the second nip N 2 of the calender, takes place while the first nip N 1 is open. The threading into the second nip N 2 can be carried out, for example, either by means of an auxiliary nip formed by a small roll or by means of so-called "tail shooter" plates (these embodiments are not shown in Fig. 1). After the threading and widening of the web W, the fourth roll 16 is lowered into contact with the third roll 15, i.e. the first nip N 1 of the calender is closed. In order to produce symmetrical paper by means of the calender 10, it is also possible to provide the lowest roll in the calender, i.e. the first roll 13, with a resilient coating. In such an embodiment a so-called air doctor is installed on the first roll 13, which air doctor is not in contact with the face of the roll 13. By means of the air doctor (not shown) it is possible to doctor the web W in its full width to the pulper (not shown). In this embodiment, also the lowest nip, i.e. the third nip N 3 of the calender, is open during the threading of the web W, and during the threading the lead-in strip is guided to the pulper by means of blows. Especially by means of the calender solution described above, in which both the topmost and the lowest roll 16,13 in the stack of rolls are provided with a resilient coating, it is possible to obtain the same advantages as are essential in the soft calender. These achieved advantages include better printing quality, high gloss, which is achieved by means of high temperatures, better strength qualities and better toughness and bulk and, further, better control of the quality of both sides of the paper. Since, compared to the soft calenders, the calender 10 in accordance with the invention has additionally the middle nip, i.e. the second nip N 2 , which is a hard nip formed by the hard-faced rolls 14,15, it is better possible to even the caliper by means of this hard nip N 2 . Control of the caliper comparable to a hard-nip calender in accordance with the invention is not possible by means of a soft calender, so that the calender 10 in accordance with the invention can be considered superior to the soft calenders. If the raw paper is unequalsided, i.e. if a separate press has not been used in the press section of the paper machine, it is possible to provide only the mantle of the upper, i.e. the fourth roll 16, of the calender 10 in accordance with the invention with a resilient coating. Concerning the solution in accordance with Fig. 1, it can be still stated briefly that the loading cylinders 33,41 for loading of the loading arms 30,38 of the third and the fourth roll 15,16 in the calender can be either hydraulic or pneumatic cylinders. By means of these loading arms 30,38 and loading cylinders 33,41, the raising of the rolls 15,16 to the service position and the raising of the rolls 16 or 15 and 16 into twin-nip operation or single-nip operation, which will be described in more detail later, are also arranged. Fig. 1 shows the running of the web W into the calendering nips quite schematically and by way of example by means of the guide and reversing rolls 42,43. In stead of these, alternative solutions suitable for the purpose can, of course, also be used. Figs. 2A,2B and 2C as well as 3A,3B and 3C show alternative solutions for different modes of operation of a calender 10 in accordance with the invention, and in the following it will be described fully by way of example, how a wide adjustability of the linear loads can be achieved by means of a solution in accordance with the invention. Fig. 2A shows the set of rolls of the calender 10 in accordance with the invention, the rolls 13,14,15,16 being arranged in a way similar to Fig. 1, so that all the nips N 1 ,N 2 ,N 3 between the rolls are closed. Thus, in this embodiment, the calender 10 is operated with three nips. With such a mode of operation, it is possible to show by way of example that, in the adjustability of the linear loads in the nips N 1 ,N 2 ,N 3 , the following values are reached, which are merely exemplifying numerical values illustrating the width of the ranges of adjustment. If the calender concerned is relatively narrow, whose web width is of an order of 7000 mm, the linear loads in the nips N 1 ,N 2 ,N 3 are adjustable within the following limits: the range of variation of the linear load in the first nip N 1 is 13...91 kN/m, the range of variation of the linear load in the second nip N 2 is 30...108 kN/m, and the range of variation of the linear load in the third nip N 3 is 52...130 kN/m. If the calender 10 is again constructed wide and the web width is, for example, 9300 mm, the ranges of variation of linear loads in the nips N 1 ,N 2 ,N 3 are as follows: the first nip N 1 25...85 kN/m, the second nip N 2 45...105 kN/m, and the third nip N 3 70...130 kN/m. Fig. 2B shows a situation of running the calender 10 with two nips. Then, the topmost roll in the calender stack, i.e. the fourth roll 16, has been raised by means of the loading arms 38 and the loading cylinder 41, so that the first nip N 1 is open. Thus, in this embodiment, the fourth roll 16 does not affect the paper web W in any way, but the web is passed over the third roll 15 only through the second nip N 2 and the third nip N 3 in the calender. Then, the linear loads in the nips N 2 and N 3 are adjustable in the following way. The linear load in the narrow calender described above, in the nip N 2 between the second and the third roll 14,15, is of an order of 17 kN/m, and it is adjustable between 39...130 kN/m in the nip N 3 between the first and the second roll 13,14. Correspondingly, the wide calender described above has a nip load of an order of 20 kN/m in the nip N 2 between the second roll 14 and the third roll 15, and an adjustable nip load between 45...130 kN/m in the nip N 3 between the first roll 13 and the second roll 14. On the other hand, Fig. 2C shows a situation of running the calender 10 with one nip. In addition to the embodiment shown in Fig. 2B, also the third roll 15 in the stack of rolls has been raised by means of the loading arms 30 and the loading cylinders 33 so that both the first nip N 1 and the second nip N 2 in the stack of rolls are open. In this embodiment, the paper web W is passed only through the nip N 3 between the first roll 13 and the second roll 14. In said nip, similarly to the embodiments described above, the linear loads are adjustable in a narrow calender construction between 15...110 kN/m, and it is also possible to reach the same adjustability, i.e. 15...110 kN/m, by means of a wide calender construction. Compared to the solution illustrated in Fig. 2A, the lowering of the lower limit of the adjustment ranges in the solutions of Figs. 2B and 2C is naturally derived from the fact that, in Figs. 2B and 2C, the weights and/or loadings of the upper rolls do not affect, or add to, the loading pressures in the nips between the lower rolls. Further embodiments for the adjustability of the linear loads in the nips N 1 ,N 2 ,N 3 in the calender 10 in accordance with the invention are shown in Figs. 3A,3B and 3C. The situation in accordance with Fig. 3A corresponds to the basic construction presented in Figs. 1 and 2A, so that, in the case of Fig. 3A, the linear loads in the nips N 1 ,N 2 ,N 3 are adjustable in a way similar to that described in relation to Fig. 2A. On the contrary, the solution in Fig. 3B is essentially different from the embodiments described above. In the solution in accordance with this figure, the axle 35 of the topmost, i.e. the fourth roll 16, in the stack of rolls is mounted in the bearing housings 37 so that it is possible to rotate said axle 35 through 180 degrees in relation to the centre axis of the roll 16. Fig. 3B shows exactly a situation in which the rotating of the axle 35 of the roll 16 has taken place, whereby the hydraulic loading devices 36 in the fourth roll 16 are still in the nip plane of the stack of rolls, but they no longer load the first nip N 1 , but they act in the opposite direction away from the nip N 1 . By means of such a solution, it is possible to achieve the following linear load levels in the nips N 1 ,N 2 ,N 3 , with reference to the examples illustrated in Figs. 2A,2B,2C. In the first nip N 1 the linear loads are of an order of 15 kN/m both in a narrow and in a wide calender construction. Correspondingly, in the second nip N 2 , it is possible to achieve a linear load of an order of 32 kN/m with a narrow calender construction and of an order of 35 kN/m with a wide calender construction. Similarly, the linear load range in the nip N 3 between the first roll 13 and the second roll 14 in the stack of rolls is, with a narrow calender construction of an order of 54...130 kN/m and, with a wide calender construction, 60...130 kN/m. The embodiment in accordance with Fig. 3C differs from those described above in the respect that, in the calender in accordance with this figure, the axle 22 of the second roll 14 in the stack of rolls is mounted in the bearing housings 24 so that it is possible to rotate said axle 22 through 180 degrees in relation to the centre axis of the roll 14. In the illustration of Fig. 3C, the rotating of the axle 22 of the roll has taken place, after which, differing from Fig. 3A, the hydraulic loading devices 23 of the roll 14 do not load the nip N 3 between the first roll 13 and the second roll 14 in the stack of rolls, but, instead, they load the nip N 2 between said second roll 14 and the third roll 15. In stead, differing from fig. 3B, in the embodiment of Fig. 3C, the hydraulic loading elements 36 of the topmost, i.e. the fourth roll 16, load the nip N 1 between the third roll 15 and the fourth roll 16. According to the exemplifying embodiments described above, it is possible to reach the following linear load levels by means of the solution in accordance with Fig. 3C. In the nip N 1 between the fourth roll 16 and the third roll 15, the linear load levels will be, in a narrow calender construction, in the range of 13...97 kN/m and, in a wide calender construction, between 25...85 kN/m. In the nip N 2 between the third roll 15 and second roll 14, the linear load levels are correspondingly, in a narrow calender construction, in the range of 30...114 kN/m and, in a wide calender construction, 45...110 kN/m. In the nip N 3 between the second roll 14 and the first roll 13, the linear loads are again, in both narrow and wide calender constructions of an order of 15...130 kN/m. The possibility which was brought up in the description above, to rotate the axles 22,35 of the second roll 14 and the fourth roll 16, brings, as was described above, a remarkable improvement to the adjustability of the linear loads in the nips N 1 ,N 2 , N 3 . It is possible to carry out the rotating of the axles 22,35 of the rolls 14,16 manually, or the axles of said rolls can be provided with a suitable drive gear, such as a motor or equivalent, by means of which it is possible to carry out the rotating of the axles. Further referring to the description above, the given linear load levels are merely examples, attempting to illustrate how a wide adjustability of the linear loads is achieved by means of a calender in accordance with the invention. However, it should be noticed that the given numerical values are related to certain calender constructions only, so that the adjustability of the linear loads of a calender in accordance with the invention is by no means restricted to these numerical values. By means of other calender constructions, it is possible to produce linear load ranges which differ from the given values even considerably. By means of a calender in accordance with the invention, it is possible to achieve substantially all the advantages that it is possible to achieve by means of conventional soft calenders, as was already stated earlier. In relation to soft calenders, the further advantage is obtained by means of the solution in accordance with the invention, that, in a calender in accordance with the invention, the middle nip N 2 is a hard nip which evens out the caliper. It is not possible to achieve corresponding evening out of the caliper by means of conventional soft calenders. It has also been stated in the description above that, in a basic solution of the invention, the two lowest rolls 13,14 in the stack of rolls in the calender 10 are driven rolls. The topmost roll 16 in the stack of rolls can also be provided with a drive gear. Above, the invention has been described by way of example with reference to the figures in the accompanying drawing. The invention is, however, not confined to the exemplifying embodiments illustrated in the figures alone, but different embodiments of the invention may show variation within the scope of the inventive idea defined in the accompanying claims.

Claims: A calender, comprising a calender frame (11,12) and a stack of rolls mounted on the frame and consisting of four rolls (13,14,15,16) fitted one above the other, in which stack the rolls placed one above the other can be fitted in nip contact with one another so as to calender the paper web (W) or equivalent in said nips (N 1 ,N 2 ,N 3 ), and which stack of rolls comprises variable-crown rolls (13,14,16), of which rolls the roll mantle (17) of at least one roll (13) can be displaced in relation to the roll axle (18) in the direction of the nip plane by means of loading devices (19) fitted inside said roll, and one heatable roll (15), which is fitted between two variable-crown rolls (14,16) in the stack of rolls, wherein the first roll (13) from the bottom of the stack and the fourth roll (16) from the bottom of the stack of rolls are variable-crown rolls, the third roll (15) from the bottom of the stack of rolls is a heatable roll, and the axles (18,22) of the first and the second roll (13,14) from the bottom of the stack of rolls are mounted on the calender frame (11,12) stationary in the direction of the nip plane, and that the third and the fourth roll (15,16) from the bottom of the stack of rolls are mounted on the calender frame (11,12) so that their axles (27,35) can be displaced in the direction of the nip plane, characterized in that the second roll (14) from the bottom of the stack is a variable-crown roll. A calender as claimed in claim 1, characterized in that the roll mantle (17) of the first roll (13) from the bottom of the stack of rolls is arranged to be radially displaceable in relation to the roll axle (18) in the direction of the nip plane. A calender as claimed in claim 1, characterized in that the roll mantles (17,21,34) of all the variable-crown rolls (13,14,16) in the stack of rolls are radially displaceable in relation to the axle (18,22,35) of the roll concerned in the direction of the nip plane. A calender as claimed in any of the preceding claims, characterized in that the variable crown rolls (13,14,16) in the stack of rolls are adjustable in zones. A calender as claimed in any of the preceding claims, characterized in that the third and the fourth roll (15,16) from the bottom of the stack of rolls are mounted on the calender frame (11,12) by means of loading arms (30,38) and loading cylinders (33,41). A calender as claimed in any of the preceding claims, characterized in that the fourth roll (16) from the bottom of the stack of rolls in the calender (10) can be displaced in order to open the nip (N 1 ) between said fourth roll (16) from the bottom of the stack and the third roll (15) from the bottom of the stack, in which case the web (W) can be passed only through the nip (N 2 ) between the third and the second roll (15,14) from the bottom of the stack and through the nip (N 3 ) between the second and the first roll (14,13) from the bottom of the stack in order to calender the web (W) in said two nips. A calender as claimed in any of claims 1-5, characterized in that the third and the fourth roll (15,16) from the bottom of the stack of rolls in the calender (10) can be displaced in order to open the nip (N 1 ) between said rolls and the nip (N 2 ) between the third and the second roll (14,15) from the bottom of the stack, in which case the web (W) can be passed only through the nip (N 3 ) between the second and the first roll (14,13) from the bottom of the stack in order to run the calender with one nip. A calender as claimed in any of the preceding claims, characterized in that at least the first and second roll (13,14) from the bottom of the stack of rolls in the calender (10) are driven rolls. A calender as claimed in any of the preceding claims, characterized in that the rolls (13,14,15,16) in the calender (10) are hard rolls. A calender as claimed in claim 8, characterized in that also the fourth roll (16) from the bottom of the stack of rolls is a driven roll. A calender as claimed in claim 10, characterized in that the fourth roll (16) from the bottom of the stack of rolls is provided with a resilient roll coating. A calender as claimed in claim 11, characterized in that in order to achieve a symmetrical paper web (W), the first roll (13) from the bottom of the stack of rolls is also provided with a resilient roll coating. A calender as claimed in any of the preceding claims, characterized in that in order to extend the adjustability of the level of linear loads in the calendering nips (N 1 ,N 2 ,N 3 ), the axle (35) of at least the fourth roll (16) from the bottom of the stack of rolls is mounted on the calender (10) so that it can revolve through 180 degrees in the axial direction of the roll so that the loading devices (36) that are inside said fourth roll (16) from the bottom of the stack can be turned away from loading the nip (N 1 ) between the fourth roll (16) from the bottom of the stack and the third roll (15) from the bottom of the stack into the opposite direction. A calender as claimed in any of the preceding claims, characterized in that in order to extend the adjustability of the level of linear loads in the calendering nips (N 1 ,N 2 ,N 3 ), the axle (22) of at least the second roll (14) from the bottom of the stack of rolls is mounted on the calender (10) so that it can revolve through 180 degrees in the axial direction of the roll so that the loading devices (23) that are inside said second roll (14) from the bottom of the stack can be turned to load either the nip (N 3 ) between the second roll (14) from the bottom of the stack and the first roll (13) from the bottom of the stack or the nip (N 2 ) between the second roll (14) from the bottom of the stack and the third roll (15) from the bottom of the stack. A calender as claimed in claim 13 or 14, characterized in that the axles (22,35) of the rolls (14 and/or 16), which axles are mounted so that they can be rotated, can be rotated manually. A calender as claimed in claim 13 or 14, characterized in that the axles (22,35) of the rolls (14 and/or 15), which axles are mounted so that they can be rotated, are provided with a rotating motor or equivalent.

Inventors: KORHONEN VILLE, PIRINEN TIMO, RAMSTEDT JORMA, KORHONEN, VILLE, PIRINEN, TIMO, RAMSTEDT, JORMA
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1994
Main classification: D21G1
IPC codes: D21G1